In 1873 Italy, Camillo Golgi created the black reaction technique, which enabled scientists to stain and view the structure of neurons, the specialized cells that compose the nervous system. During the nineteenth century, scientists were studying cells and proposed cell theory, which describes the basic characteristics of cells as fundamental units of life. However, cell theory struggled to explain neurons as they are specialized cells and more complex in structure than cells of other tissues. Prior to Golgi’s black reaction, other neuron staining techniques did not enable scientists to clearly and completely view entire neurons without damaging the tissue and obscuring the form. By enabling scientists to study individual neurons and neural tissues, Golgi’s black reaction enables researchers to better study the nervous system and how it develops.

The neuron doctrine is a concept formed during the turn of the twentieth century that describes the properties of neurons, the specialized cells that compose the nervous system. The neuron doctrine was one of two major theories on the composition of the nervous system at the time. Advocates of the neuron doctrine claimed that the nervous system was composed of discrete cellular units. Proponents of the alternative reticular theory, on the other hand, argued that the entire nervous system was a continuous network of cells, without gaps or synapses between the cells. In 1873, physician and reticular theory supporter Camillo Golgi developed a staining technique called the black reaction, a neuron staining technique that allowed for complete visibility of nerve cells, which enabled scientists to view a complete neuron cell and its cellular structures. Later, neuroscientist Santiago Ramón y Cajal used the black reaction to show the existence of synapses, or gaps between neurons, and argued that his evidence supported the neuron doctrine. The confirmation of the neuron doctrine showed that neurons function as discrete and independent cells, not as a single network, within the nervous system.

In the nineteenth century, reticular theory aimed to describe the properties of neurons, the specialized cells which make up the nervous system, but was later disconfirmed by evidence. Reticular theory stated that the nervous system was composed of a continuous network of specialized cells without gaps (synapses), and was first proposed by researcher Joseph von Gerlach in Germany in 1871. Reticular theory played a significant role in developmental neurobiology as it enabled scientists to theorize how the form of neural cells functioned in the context of the broader nervous system, and although disproven, reticular theory contributed to the foundation of the neuron doctrine that informed the modern field of neurobiology.